1. Field of the Invention
The present invention relates to a polymer compound for an electrode material, an electrode using the polymer compound and a nonaqueous solution battery using the polymer compound.
2. Description of the Related Art
In these years, there has been increased demand for batteries having high energy density. As one of such batteries, there can be cited a lithium battery having a high voltage as a single cell. According to the lithium battery, use of a nonaqueous electrolytic solution makes it possible to obtain a high voltage of 3 V or more; however, the capacities per weight of the positive and negative electrode materials are not necessarily sufficient in a manner such that a capacity of 140 to 150 mAh/g is obtained in the case of cobalt lithiumate used for a positive electrode.
Accordingly, there have been made various investigations on the positive and negative electrode materials which can make larger the capacities per weight of the positive and negative electrodes, respectively; as for the positive electrode, some of these materials being investigated are oxides of metals including manganese, iron and niobium, any of which is large in weight and small in the number of reactive electrons so that a large capacity can hardly be obtained.
The investigations also involve the application of conducting polymers including polyaniline as the positive electrode materials because these polymers are light in weight; however, the number of reactive electrons per unit molecular weight of polyaniline is 0.5 and the capacity per weight of polyaniline is about 145 mAh/g, which is not much larger than the above described capacity of cobalt at lithiumate.
On the other hand, there has been known an application, as a positive electrode material, of an organo-sulfur polymer compound as a polymer compound capable of yielding a high capacity and a high energy density (see, for example, U.S. Pat. No. 4,833,048; J. Electrochem. Soc., Vol. 136, pp. 661 to 664 (1989); J. Electrochem. Soc., Vol. 136, pp. 2570 to 2575 (1989)).
The organo-sulfur polymer compound has S—S bonds in the main chain thereof, the polymer compounds being represented by R—S—S—R. The organo-sulfur polymer compound undergoes a reversible redox reaction in which organic thiolates (R—SH) are formed in the reduced state thereof with the cleaved S—S bond, and the organic thiolates are in turn bonded in the oxidized state to regenerate the S—S bond. Accordingly, when the organo-sulfur polymer compound is used as a positive electrode material, the polymer compound can conduct charge/discharge by making use of the redox reaction.
However, the organo-sulfur polymer compound has a large difference between the oxidation potential and the reduction potential so as for the reaction rate to be made slow, leading to a disadvantage that the operation temperature is needed to be elevated to a temperature of 100° C. or higher when operation as a battery is made to come into effect. When the organo-sulfur polymer compound is reduced into the organic thiolate, the molecular weight of the compound is made smaller, and hence the compound is dissolved in the electrolytic solution to diffuse outside the electrode, leading to a disadvantage that the capacity degradation tends to be caused.